Holley idle mixture screws

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Oct 23, 2011 | 07:41 PM

68vetteman

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Racer

Joined: Oct 2007

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From: Palm PA

Holley idle mixture screws

I know every carb and car is different but can anybody give me a ballpark number for the idle mix screws for a 700 double pumper. My screws are backed out 1 turn. The car runs good but it surges when slowing to a stop with my foot off of the gas. Could running too lean cause the surging?

68 Vetteman

Oct 23, 2011 | 08:20 PM

PeteZO6

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From: Cameron Park CA

Check your float levels. ~1 turn is in the ball park as I recall.

Pete

Oct 23, 2011 | 08:37 PM

68vetteman

Thread Starter

Racer

Joined: Oct 2007

Posts: 284

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From: Palm PA

Quote:

Originally Posted by PeteZO6

Check your float levels. ~1 turn is in the ball park as I recall.

Pete

The fuel level is good. I have just a little trickle of gas with the engine running and the plugs off. I have a roller cam with 270 duration on intake and 276 duration on the exhaust. I have a steady idle at 900 rpm. Is the surging normal with a cam like this?
68 Vetteman

Oct 23, 2011 | 09:04 PM

Mako72

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On my 650 DP, I used a vacuum gauge to set the mixture.

http://www.holley.com/TechService/FA...ory=Carburetor

Oct 23, 2011 | 11:07 PM

scottyp99

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From: Oxford MA-----You just lost the game!!!!

Quote:

Originally Posted by 68vetteman

Back them out another 1/4 turn and see how it runs.

Scott

Oct 24, 2011 | 06:32 PM

PeteZO6

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From: Cameron Park CA

Quote:

Originally Posted by 68vetteman

If that is the duration at 0.050, it is a pretty stout cam which would give you a noticable lope at idle, but not it shouldn't surge if all else is right. Others will chime if I'm wrong on that.

Oct 24, 2011 | 08:55 PM

Solid LT1

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From: Fremont CA

Quote:

Originally Posted by Mako72

On my 650 DP, I used a vacuum gauge to set the mixture.

http://www.holley.com/TechService/FA...ory=Carburetor

Vacuum guage is the method I use. There is a relationship between, initial timing, fuel mixture, and idle speed. Advancing the timing will increase idle speed. Most motors run best between 8-14degrees BTDC at idle (but, its hell on emissions.) Get timing set, adjust idle mixture screws with vacuum guage, then set idle RPM. Your looking for highest idle vacuum reading, accomplished by setting mixture screws from rich to lean. I ballpark mixture screws 1.5-1.75 turns out from full bottom. You should also beware that there are Holley metering blocks out there with backwards idle screws (mostly oddball mid 70's economy designs) where full in is fully rich mixture. Hope this helps you.

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